Dynamics of auto- and heterotrophic picoplankton and associated viruses in Lake Geneva

Abstract

Abstract. Microbial dynamics have rarely been investigated in Lake Geneva, known as the largest lake in western Europe. From a 5-month survey, we report dynamic patterns of free-living virus, bacteria and small phytoplankton abundances in response to a variety of environmental parameters. For the first time, we fractionated the primary production to separate the contribution of different size-related biological compartments and measured both bacterial and viral production in addition to experiments conducted to quantify the virus-induced bacterial mortality. We observed marked seasonal and vertical variations in picocyanobacteria, bacteria and virus abundances and production. The contribution of picoplankton and nanoplankton production to the total primary production was high (reaching up to 76 % of total primary production) in November and the spring-summer transition period, respectively. The impact of viral lysis on both bacteria and picocyanobacteria was significantly higher than grazing activities. Virus-induced picocyanobacterial mortality reached up to 66 % of cell removal compared to virus induced (heterotrophic) bacterial mortality, which reached a maximum of 34 % in July. Statistical analyzes revealed that temperature and top-down control by viruses are among important factors regulating the picocyanobacterial dynamics in this lake. More generally speaking, our results add to the growing evidence and accepted view nowadays that viruses are an important actor of freshwater microbial dynamics and more globally of the functioning of the microbial food webs.

Deciphering the virus‐to‐prokaryote ratio (VPR): insights into virus–host relationships in a variety of ecosystems

“…Consequently, it has been posited that declines in VBR are due to viral loss, for example by non-specific adsorption to particles (Maranger & Bird, 1995) or degradation after adsorption to humic substances (Anesio et al, 2004). Inversely, high VBR values have been attributed to high viral production Kellogg, 2010;Yoshida-Takashima et al, 2012;Pinto, Larsen & Casper, 2013;Engelhardt et al, 2014;Parvathi et al, 2014) or low viral decay (Mei & Danovaro, 2004;Danovaro et al, 2005;Williamson et al, 2007;Winter, Kerros & Weinbauer, 2009;Maurice et al, 2010;De Corte et al, 2012), which in some cases (e.g. in soil and sediments) could be an artifact of extraction procedures (Middelboe, Glud & Finster, 2003;Williamson, Radosevich & Wommack, 2005;Kimura et al, 2008;Williamson, 2011).…”

Prevalence of Viral Photosynthetic and Capsid Protein Genes from Cyanophages in Two Large and Deep Perialpine Lakes

“…During the last decade, previous studies have partially identified the diversity, dynamics, or role (as mortality agents of picocyanobacteria) of cyano(myo)phages in French perialpine lakes (12,17,23,42,43). This body of work has suggested that the cyano(myo)phage community is diverse, displays marked seasonal variations, and is concentrated mainly in surface waters down to 20 m deep.…”

Spatial and temporal dynamics of virioplankton in a high mountain tropical reservoir, El Neusa (Cundinamarca, Colombia)

“…A positive association would be explained by a direct dependence of the phages by the density of its main host, as previously described in a large number of ecosystems (e.g., De Araújo & Godinho, 2009;Barros et al, 2010;Ram et al, 2011;Ben Rhomdame et al, 2014;Parvathi et al, 2014). However, this relationship could be partially darkened by the interaction of other biological components, such as mixotrophic and heterotrophic nanoflagellates, which have been detected as important agents of bacterioplankton mortality (Hakspiel-Segura, 2005).…”